Variable resistor unit



June 2,1936. P. KOTOWSKI 2,042,606

V VARIABLE RES ISTOR UNIT Filed May 11, 1953 INVENTOR 1 ,4 UL KOTOWS/f/ ATTbRNEY Patented June 2, 1936 VARIABLE RESXS'IQR UNIT Paul Kotowski, Berlin, Germany,

assignmto Telefunken Gesellschaft fiir lirahtlose Telegraphic m. b. H., Berlin, Germany, a corporation of Germany Application May 11, 1933, Serial No. 679,42;

In Germany May 26, 1932 2 Claims.

For a great many purposes, especially in broadcast and in amplifier work it is necessary to use resistances the value of which is a function of the mechanical pressure applied thereto. Of particularly great importance are resistances of the said kind in connection with electrical music instruments inasmuch as by the use thereof it is possible to render the musical instrument capable of being played and operated in a way as usual with mechanical instruments. Furthermore, resistances of the said sort could be used also for measuring purposes, say, weighing, -pressure metering in gases and liquids, pressure measurements in machine-tools, etc.

The resistances depending for their operation upon pressure most widely known in the prior art.

are carbon-grain or dust resistances of the type employed, for example, in microphones. The demerits of such resistances are that they lack constancy or stability, and that caking together of the granules is liable to happen which frequently leads to short-circuiting and burning of the resistor body. What is also disagreeably felt is the inevitable roaring noise as well as the low ohmic value of the resistor, a fact that becomes particularly disagreeable when it is connected in amplifier circuit arrangements.

It is accordingly an object of the present invention to provide a resistor material which substantially avoids the cheats mentioned.

It is a further object of the invention to provide a resistor in which the material is in a pulverulent or finely powdered condition and is embedded or attached to a yieldable material which supports it.

Other objects of the invention will become apparent to those skilled in the art as the description thereof proceeds. For a better understanding of the invention reference is made to the attached drawing in which;

Fig. 1a. is an isometric view of a yieidable resistor made according to the invention;

Fig. 1b is a much enlarged view of a small portion of the device of Fig. 1a;

Fig. 2a is an enlarged view of a modified form of the invention; and,

Fig. 2b is an enlarged view of a small portion of the device of'Fig. 2a.

Now, according to the present invention the above-mentioned drawbacks are avoided in that the pressure-dependent resistance is made of resistor material in pulverulent or granular state embedded or incorporated in a yielding material or placed upon a material being yieldable because of its structure and/or other properties. What may be considered for practical use as the said elastic material are natural resins (rubber, gum or gum-like substances), albumen or albuminous compounds (gelatin, casein), cellulose derivatives (celluloid, nitro-cellulose, cellulose acetate), or the like. material may be made of any electrical conductive material, it being not necessary in this connection for this material itself to possess the properties of pressure-dependent resistance. The reduction of resistance as a result of compression, in the case of materials not responsive to pressure actions, may beascribed to the fact that upon the arising of pressure or compression, the number of paralleled contacts or contacting areas of the adjacent particles grows. When using carbon dust or grains in a yielding material, however, it is likely that the pressure-response pure and simple in the resistancematerial plays a decisive part. The manufacture of such a resistance occurs in this manner that the resistance material is mixed with or incorporated in the liquid or semi-liquid supporting body or matrix; and after solidification thereof, there is obtained the desired pressure-dependent or pressure-responsive resistance.

Inasmuch as for certain purposes the range of regulation is inadequate, according to a further object of the invention arrangements are so made that the pulverulent or granular resistance material is brought upon a cotton or other iloccular support. For saturated with a rubber solution, upon which graphite, bone dust, microphone carbon or else metallic powder is brought. The cotton or other flocculent base body may consist of any desired non-conducting materials, for instance, glass, cellulose, cotton, silk, rubber, or the like made into the form of filaments. But the resistance material could be applied also upon a uniform and homogeneous body possessing high elasticity and resiliency such as a rubber sponge.

The drawing shows a number of exemplified embodiments of the basic idea of the invention. Fig. 1a shows a pressure-dependent resistance made of yielding material in which the resistor material itself is incorporated or embedded. Fig. lb shows the arrangement of the resistor material in the supporter or vehicle medium drawn to an enlarged scale; The constituent resistor granules i are held together by schematically illustrated bands 2, the resistor material chosen in this instance being granular carbon. The constituent particles are placed, as will be seen, at close The pulverulent or granular resistor instance, absorbent cotton is.

there is merely used the porperty of carbon that its conductivity experiences a change when being compressed. Fig. 2a shows the disposition oi. the resistor powder upon the difierent threads or fibers of a cotton or other fiocculate'supporter body. Fig. 2b is an enlarged schematic representation of the arrangement of the resistor bodies upon the difl'erent threads I. Resistor particles 3, even when not subject to compression or under pressure, are already in contact. Upon compression alteration of the resistance value is only obtained when the resistance body itself is pressure responsive. The situation is different in the case of resistance bodies 4 and '5. These latter are caused to come in contact with each other, and thus new paths of flow tor the current are opened up. As the pressure is further increased an effect will become noticeable at I and 5 only when these parts are made of pressure-responsive resistor proximity or in contact. By a compressive action material, while particles 6 come to make direct contact. The summation of all 0! these etl'ects has this result that the resistance unit is capable v being compressed relatively strongly so that a larger range 01' regulation is feasible.

I claim:

1. A variable resistor unit comprising rubber formed into a plurality ofiilamentary bodies, and a coating surrounding said bodies, said coating consisting of a mixture of rubber solution and fine particles of pulverulent conducting material.

2. A variable resistor unit comprising a plurality of filamentary bodies composed of rubber and a pluralityof particles of pulverulent conducting material attached to said bodies, at least some of said particles having their adjacent surfaces in contact when no external pressure is applied to said resistor unit.

. PAUL KO'IOWSKI. 

